Subterranean pipes and conduits such as sewers have been repaired and/or rehabilitated using a number of techniques. One approach that avoids the need for excavation is a process that involves everting a resin impregnated lining tube into the underground pipe using fluid pressure, expanding the tube with fluid pressure, and then curing the tube in place against the interior surface of the sewer pipe. Although this technique has been used for a number of years and has worked well for the most part, it has not been wholly free of problems.
For example, when everting the lining tube into the sewer pipe, significant friction forces must be overcome. As exemplified by U.S. Pat. No. 6,390,795 to Waring et al., the lining tube is typically flattened and extended through a linear slot. The slot must provide a seal that is tight enough to maintain adequate pressure for everting the tube, while the seal must not be so tight that the frictional forces are unduly high. Using a linear slot such as in the Waring patent has proven to be problematic because the seal applies so much friction that there is an excessive restraint on pulling of the liner into the sewer pipe.